Effects of Disbonds, Lightning Strikes, and Low-Velocity Impact Damage on Adhesively Bonded ...

146 Pages·2009·12.38 MB·English

by  Waruna P. Seneviratne

DOT/FAA/AR-09/4 Effects of Disbonds, Lightning

Strikes, and Low-Velocity Impact
Air Traffic Organization
NextGen & Operations Planning
Office of Aviation Research and Damage on Adhesively Bonded
Technology Development

Washington, DC 20591
Composite Joints

December 2009

Final Report

This document is available to the U.S. public
through the National Technical Information
Service (NTIS), Springfield, Virginia 22161.

U.S. Department of Transportation
Federal Aviation Administration
NOTICE

This document is disseminated under the sponsorship of the U.S.
Department of Transportation in the interest of information exchange. The
United States Government assumes no liability for the contents or use
thereof. The United States Government does not endorse products or
manufacturers. Trade or manufacturer's names appear herein solely
because they are considered essential to the objective of this report. This
document does not constitute FAA certification policy. Consult your local
FAA aircraft certification office as to its use.

This report is available at the Federal Aviation Administration William J.
Hughes Technical Center’s Full-Text Technical Reports page:
actlibrary.act.faa.gov in Adobe Acrobat portable document format (PDF).
Technical Report Documentation Page
1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
DOT/FAA/AR-09/4
4. Title and Subtitle 5. Report Date
EFFECTS OF DISBONDS, LIGHTNING STRIKES, AND LOW-VELOCITY December 2009
IMPACT DAMAGE ON ADHESIVELY BONDED COMPOSITE JOINTS 6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.
John Tomblin, Waruna Seneviratne, and Govind Ramakrishna Pillai
9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)
Department of Aerospace Engineering
Wichita State University 11. Contract or Grant No.

Wichita, KS 67260-0093
12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered
U.S. Department of Transportation Final Report
Federal Aviation Administration
Air Traffic Organization NextGen & Operations Planning 14. Sponsoring Agency Code
ACE-110
Office of Research and Technology Development
Washington, DC 20591
15. Supplementary Notes
The Federal Aviation Administration Airport and Aircraft Safety R&D Division COTR was Curtis Davis.
16. Abstract
Development of advanced material and process technologies has significantly increased the use of adhesively bonded joints in
aircraft structures due to the favorable characteristics of these joints compared with riveted, spot-welded, and mechanically
fastened structures. Joints, doublers, sandwich constructions, and repair patches are some examples of bonded applications in
aircraft primary structures. Applications on structures require rigorous characterization of the adhesive joints. Short- and long-
term issues must be investigated so the certification of these joints can be instituted to ensure their structural integrity throughout
the service life of the aircraft. For the damage tolerance design philosophy of adhesively bonded joints, it is vital for adhesive
joints to demonstrate no-growth behavior with the presence of a discrete damage. There is also a need to demonstrate the ability
of adhesive joints to contain larger amounts of damage or disbond that might be incurred during flight or production without
catastrophic failure. Although the effects of defects on laminated composite and sandwich construction have been investigated in
detail, limited studies have been conducted in the area of impact damage on bonded joints.

The purpose of this research was to investigate the static strength of adhesively bonded composite joints with the presence of
large damage. The research addressed the concerns related to manufacturing and operational defects of bonded joints, i.e.,
different disbond geometries, lightning strike damages, fail-safe fastener installation, and low-velocity impact damages, and their
impact on static strength. Specimens that were impacted with various impactor diameters and energy levels were subjected to
shear and tensile loading using picture-frame shear and single-lap shear test configurations. The other defects were only
addressed using picture-frame shear loading configuration.

Test data show that a rectangular defect that spreads completely across the joint overlap region results in approximately 20%
reduction in shear strength. Rectangular defects repaired with fasteners completely restored the original strength of the bonded
joint. In contrast to rectangular defects, the circular- and diamond-shaped defects and through holes that are continued within the
elastic trough had minimal effect.

The results of picture frame tests with specimens impacted at the 270 in-lbf energy level show a 20% reduction in shear strength.
Because all the single-lap specimens with and without impact damage failed in the adherend, the shear strength was the same,
irrespective of impact energy or impactor diameter.

The results from this research will aid in increased use of adhesive joints in structures and help establish inspection and
maintenance practices.

17. Key Words 18. Distribution Statement
Adhesive, Defects, Impact, Disbond, Debond This document is available to the U.S. public through the
National Technical Information Service (NTIS), Springfield,
Virginia 22161.
19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price
Unclassified Unclassified 146

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
ACKNOWLEDGEMENTS
The authors would like to acknowledge the technical guidance and support of Mr. Curtis Davis,
Dr. Larry Ilcewicz, and Mr. Peter Shyprykevich (retired) of the Federal Aviation Administration.
The support of Mr. Shin-Liang Mah and the staff of the Structures Laboratory of the National
Institute for Aviation Research was greatly appreciated during the tests and data analysis.
iii/iv
TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY xiii

1. INTRODUCTION 1
2. EXPERIMENTAL PROCEDURE 2
2.1 The EOD Investigation 3
2.2 Effects of Low-Velocity Impact Investigation 9
2.2.1 The PFS Test 9
2.2.2 The SLS Test 10

2.3 Materials 12
2.3.1 Adhesive 12
2.3.2 Adherends 12

2.4 Specimen Fabrication 12
2.5 Experimental Procedure 13
2.5.1 Impact Tests 13

2.5.2 Nondestructive Inspections 15

2.5.3 Residual Indentation Measurement 16

2.5.4 Residual Strength Tests 17

2.5.5 Full-Field, Three-Dimensional Displacement and In-Plain Strain
Measurements 19

3. RESULTS AND DISCUSSION 21
3.1 Effects of Disbonds and Lightning Strike Damages 21
3.2 The EOI Damages 29
3.2.1 The PFS Test Results 29
3.2.2 The SLS Test Results 35
3.2.3 Photomicrography of Impacted Specimens 59

4. CONCLUSIONS 76
5. REFERENCES 77
v
APPENDICES

A—Through-Transmission Ultrasound C-Scans and ARAMIS Photogrammetry Data for
Picture-Frame Shear Test Specimens

B—Single-Lap Shear Impact Test Results
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LIST OF FIGURES

Figure Page

1 Typical General Aviation Fuselage Component Showing Disbond 3

2 Lightning Strike Zone Details for Straight-Wing Business Jet 4

3 A PFS Test Specimen With a Single-Lap Joint 5

4 A PFS Test Setup 6

5 Shear-Loaded, Single-Lap Joint Section With Rectangular Disbond 6

6 Defect Geometries for EOD Investigation 8

7 The SLS Test Specimen Geometry 10

8 Gravity-Assisted Drop Tower and Support Fixture 13

9 Instron Dynatup Drop-Weight Tester 14

10 Support Fixture for SLS Impact Specimens 14

11 Impactors Used for SLS Specimens 15

12 Dynatup Impulse Data Acquisition Software 15

13 A TTU Scan of a PFS Test Specimen 16

14 Setup for Residual Indentation Depth Measurement 16

15 Depth Measurement Grid 17

16 The MTS Servo-Hydraulic Test Frame 17

17 The PFS Data Reduction 18

18 Strain Gage Installation for EOI Test Specimens 19

19 Portable Version of ARAMIS Photogrammetry System 20

20 Damage Size Assessment at Load P Using NDI Method 20

21 Effects of Overlap Length 23

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22 Comparison of EOD Test Results for 2.0-Inch Overlap 24

23 Average Failure Loads for CFPW EOD Specimens With 2-Inch Overlap 24

24 The EOD on the Stress Distribution of Bonded Joints 25

25 Photogrammetry Data for Specimen With Rectangular Defect 25

26 Failure Modes of PFS Specimens With 2- by 4-Inch (Rectangular) Defects 26

27 Comparison of Maximum SLBJ and Average Shear Stress, τ , at Failure 27
xz

28 Comparison of Far-Field Shear Stress and SLBJ Adherend Shear Stress at Failure 29

29 Summary of Failure Load for EOI Specimens With 2-Inch Overlap 32

30 Effects of Impactor Diameter With 2-Inch Overlap 32

31 Failure Loads of Impacted Specimens 33

32 Postimpact TTU C-Scan of PFS Specimen 34

33 Effects of Impactor Diameter on Damage Size 34

34 Effects of Overlap Length on Damage State 35

35 Typical Force-Displacement Curves for FGSW SLS Specimens 36

36 Typical Force-Displacement Curves for CFPW SLS Specimens 37

37 Typical Force-Displacement Curves for CFUT SLS Specimens 37

38 Typical Impact Force-Time Curves for FGSW SLS Specimens 38

39 Typical Impact Force-Time Curves for CFPW SLS Specimens 38

40 Typical Impact Force-Time Curves for CFUT SLS Specimens 39

41 Typical Total Energy-Time Curves for FGSW SLS Specimens 39

42 Typical Total Energy-Time Curves for CFPW SLS Specimens 40

43 Typical Total Energy-Time Curves for CFUT SLS Specimens 40

44 Comparison vs Time for Displacement and Impact Force for FGSW Specimens 42

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45 Impact Damage Induced on FGSW With 0.5-Inch Impactor 43

46 Impact Damage Induced on FGSW With 0.75-Inch Impactor 43

47 Impact Damage Induced on FGSW With 1.00-Inch Impactor 43

48 Impact Damage Induced on CFPW With 0.5-Inch Impactor 44

49 Impact Damage Induced on CFPW With 0.75-Inch Impactor 44

50 Impact Damage Induced on CFPW With 1.00-Inch Impactor 44

51 Impact Damage Induced on CFUT With 0.5-Inch Impactor 45

52 Impact Damage Induced on CFUT With 0.75-Inch Impactor 45

53 Impact Damage Induced on CFUT With 1.00-Inch Impactor 45

54 Ultrasonic C-Scan of FGSW (354 in-lbf) 46

55 Ultrasonic C-Scan of CFPW (354 in-lbf) 46

56 Ultrasonic C-Scan of CFUT (354 in-lbf) 46

57 Damage Area and Energy Level for FGSW 47

58 Damage Area and Energy Level for CFPW 48

59 Damage Area and Energy Level for CFUT 48

60 Residual Indentation for FGSW (354 in-lbf) 49

61 Residual Indentation for CFPW (354 in-lbf) 49

62 Residual Indentation for CFUT (354 in-lbf) 50

63 Typical Failure Mode Observed for FGSW SLS Specimens 50

64 Typical Failure Mode Observed for CFPW SLS Specimens 51

65 Typical Failure Mode Observed for CFUT SLS Specimens 51

66 Maximum Impact Force for CFUT 55

67 Maximum Residual Indentation for CFUT 55

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68 Ultimate Shear Strength for CFUT 56

69 Maximum Impact Force for CFPW 56

70 Maximum Residual Indentation for CFPW 57

71 Residual Shear Strength for CFPW 57

72 Maximum Impact Force for FGSW 58

73 Maximum Residual Indentation for FGSW 58

74 Residual Strength for FGSW 59

75 Transverse Crack Propagation 60

76 Fracture Due to Bending 60

77 Orientation of Matrix Crack Concentrations of Glass Fabric Layers (Top Adherend)
Due to Impact 62

78 Fracture Propagation on First Few Layers of Adherend Due to Impact 63

79 Photomicrograph of FGSW—I1G83C3: 0.50-Inch Impactor and 354.03 in-lbf 64

80 Photomicrograph of FGSW—I1G61C3: 1.00-Inch Impactor and 354.03 in-lbf 65

81 Photomicrograph of FGSW—I1G42B2: 0.75-Inch Impactor and 221.0 in-lbf 66

82 Photomicrograph of FGSW—I1G73B5: 0.5-Inch Impactor and 221.0 in-lbf 67

83 Photomicrograph of CFRP—I1P11C3: 1-Inch Impactor and 354.03 in-lbf 68

84 Photomicrograph of CFRP—I1P61B2: 1-Inch Impactor and 221.0 in-lbf 69

85 Photomicrograph of CFRP—I1P43B4: 0.5-Inch Impactor and 221.0 in-lbf 70

86 Photomicrograph of CFU—I1U21B3: 1-Inch Impactor and 221.0 in-lbf 71

87 Photomicrograph of CFU—I1U12B1: 0.75-Inch Impactor and 354.03 in-lbf 72

88 Photomicrograph of CFU—I1U73B2: 0.5-Inch Impactor and 221.0 in-lbf 73

89 Photomicrograph of CFU—I1U31C2: 1-Inch Impactor and 354.03 in-lbf 74

90 Photomicrograph of CFU—I1U42C2: 0.75-Inch Impactor and 354.03 in-lbf 75
x